Field
The present invention relates generally to computers having a single or multiple Central Processing Units (CPU), and more particularly, to a method and device for booting such a system directly from a storage device.
Description of Related Art
An embedded system refers to an apparatus that is made up of a single or multiple controller chips interconnected to each other on a printed circuit board. A controller chip can have one or more central processing unit (CPU) that enables it to interpret and execute code. When an embedded system has more than one processor it is already called a multiprocessor system. The term embedded system will be used to refer to a single CPU or a multiprocessor system in this paper.
A conventional embedded system contains a nonvolatile memory which is used to store firmware that is read and executed by a CPU to initialize the system. The nonvolatile memory can be a read-only memory (ROM), one-time programmable memory (OTP), programmable read only memory (PROM), electrically erasable PROM (EEPROM), or a flash PROM (FPROM). The nonvolatile memory can be internal (on-chip) or external (off-chip) to the controller chip. The firmware stored in the nonvolatile memory can be a boot code loader, a basic input/output system (BIOS), an operating system (OS), or an application firmware. The boot code loader is a small code executed by a CPU to do minimum initialization of the system. After initialization, the boot code loader copies the BIOS or OS or application firmware from a mass storage device external to the embedded system to the random access memory (RAM) of the system. When the BIOS or OS or application firmware is already loaded in the RAM, the CPU reads and executes it to do exhaustive initialization and diagnostics before proceeding to normal system operation. A mass storage device can be a rotating disk drive or a solid-state drive which is made up of FPROM devices. Though nonvolatile memory size can be reduced due to a small boot code loader, the boot code loader doesn't have the ability to self check its integrity.
In an invention described in US Patent Application Publication number US 2005/0120146 A1, Jun. 2 2005, an embedded system in FIG. 1 that does not have an on-chip nonvolatile memory such as a read only memory directly boots from flash block mass storage 106. The flash block mass storage 106 is a collection of flash chips interfaced to the flash memory controller 105. The apparatus makes use of a Flash Programming Engine, embedded within a Flash memory controller 105, the first device that is taken out of reset, to program a Direct Memory Access controller 104 to transfer a boot code loader from flash block mass storage 106 to an internal Random Access Memory (RAM) 103. When the transfer of the boot code loader to the RAM 103 is completed the internal Central Processing Unit 101 of the controller chip is taken out of reset to read and execute the boot code loader in the RAM 103. The boot code loader performs initialization of the system, power-on self tests, and copies a much larger control program or application firmware from flash block mass storage 106 to the RAM 103.